1. Field of the Invention
This invention relates to photoresist stripping liquid compositions and a method of stripping photoresists using the same. More particularly, the invention relates to photoresist stripping liquid compositions, having sufficiently good capabilities of stripping both photoresist films and modified films and inhibiting corrosion of substrates even at higher treating temperatures, to be suitably used in the fabrication of semiconductor devices such as ICs and LSIs or liquid-crystal panel devices. The invention also relates to a method of stripping photoresists using said liquid compositions.
2. Description of Relevant Art
Semiconductor devices such as ICs and LSIs as well as liquid-crystal panel devices are fabricated by a process comprising the following basic steps: forming a conductive metallic film such as a nesa film or an insulating film such as an SiO.sub.2 film onto a substrate by chemical vapor deposition or any other suitable techniques; applying a uniform photoresist layer over the metallic or insulating film; exposing the applied photoresist layer to light and developing the exposed layer to form a photoresist pattern; selectively etching the conductive metallic film or the insulating film through the photoresist pattern as a mask pattern to form a fineline circuit; and stripping away the unwanted photoresist layer with a liquid stripper. Other examples of the metallic film include those made of aluminum (Al), an aluminum alloy (Al alloy) such as aluminum-silicon (Al--Si) or aluminum-silicon-copper (Al--Si--Cu); pure titanium (Ti); or a titanium alloy (Ti alloy) such as titanium nitride (TiN) or a titanium-tungsten system (TiW). One or more of such metallic films are formed onto the substrate.
While various liquid compositions have heretofore been used to strip photoresist layers, the use of liquid systems incorporating alkanolamines was recently proposed (as in Unexamined Published Japanese Patent Applications Nos. 49,355/1987 and 208,043/1988).
In the current fabrication process of semiconductor devices and liquid-crystal devices, dry etching, ashing, ion implantation and other post-treatments are applied to photoresist films, and that it becomes necessary to strip thusly treated photoresist films. Due to those post-treatments, the photoresist films become modified in nature. With the recent increase in the strictness of the conditions for these post-treatments, the nature of the modified photoresist films tends to become inorganic than organic and, as a result, the liquid strippers using alkanolamines have turned out to be inadequate for the purpose of stripping the modified photoresist films.
More recently, liquid compositions containing hydroxylamines have been proposed as systems capable of more efficient stripping of modified photoresist films. For example, Unexamined Published Japanese Patent Application No. 289,866/1992 describes a photoresist stripping liquid composition containing both hydroxylamines and alkanolamines, and Unexamined Published Japanese Patent Application No. 266,119/1994 describes a photoresist stripping liquid composition containing not only hydroxylamines and alkanolamines but also a chelating agent (corrosion inhibitor) such as catechol.
These liquid compositions containing hydroxylamines have a greater ability to strip the modified photoresist films than the liquid strippers containing alkanolamines. However, they cause another problem in that substrates having deposited films of Al or Al alloys such as Al--Si and Al--Si--Cu, or pure titanium (Ti) are corroded. In fact, the stripping liquid composition described in Unexamined Published Japanese Patent Application No. 266,119/1994 is capable of preventing the corrosion of titanium alloys but not of pure titanium (Ti), which will suffer from progressive corrosion.
To avoid these problems, several proposals have been made as exemplified by the teaching of Unexamined Published Japanese Patent Application No. 96,911/1997, which discloses photoresist stripping liquid compositions comprising hydroxylamines, water, amines having a specific acid dissociation constant, water-soluble organic solvents and a specified amount of corrosion inhibitors. These compositions are excellent particularly in the capability of stripping modified films and exert good corrosion-inhibiting effects on substrates having films of Al, Al alloys or pure titanium (Ti) formed thereon, however, are still insufficient in the capability of stripping photoresist films.
And furthermore, in recent years, it has been required to perform the stripping at higher temperatures so as to elevate the performance efficiency. With an increase in the treating temperatures, stripping capability would be improved in general, while metallic films formed on substrates are corroded more seriously. Moreover, it has been urgently required to develop stripping liquid compositions usable in stripping both photoresist films and modified films at higher treating temperatures.
Under these circumstances, it has been desired to develop liquid photoresist strippers capable of, even at higher treatment temperatures, not only efficient strippability of both photoresist films and modified films but also effective prevention of the corrosion of substrates having metallic films, in particular those of Al or Al alloys or Ti formed thereon.
The present inventors conducted intensive studies with a view to meeting this need. As a result, they found that the need could be satisfied by using photoresist stripping liquid compositions which contain hydroxylamines, water, specified amines, dimethyl sulfoxide and aromatic hydroxy compounds in specified proportions. The present invention has been accomplished on the basis of this finding.